Motor vehicles are frequently equipped with a so-called ACC system that permits distance control, i.e. an adaptive cruise control. This system includes a distance sensor, e.g. a radar sensor or, alternatively, also a lidar sensor, with which it is possible to measure the distances to objects located in front of the vehicle. In the case of a radar sensor, it is also possible to directly measure the relative speeds. When the sensor detects a target object, e.g. a preceding vehicle, the speed of one's own vehicle is automatically adjusted so that the preceding vehicle is followed at an appropriate safety distance. When no relevant target object is detected, the speed is regulated to a desired speed selected by the driver.
In conventional systems of this type, a single radar sensor, e.g. an FMCW (frequency modulated continuous wave) radar is mounted in the middle on the front end of the vehicle, so that its optical axis coincides with the longitudinal center axis of the vehicle. The locating depth of the sensor is, for example, up to 200 m, and the locating angular range is, for example, 7° to each side of the optical axis. Within this locating angular range, the radar system has a certain angular resolution, so that based on the measured locating angle in conjunction with the measured object distance, it is possible to decide whether an object is in the same lane as one's own vehicle or in an adjacent lane. The known ACC systems in use are provided for driving with relatively high cruising speed and correspondingly large distances between vehicles on superhighways and highways that have been enlarged well, and function very reliably in this field of application. However, in traffic situations in which the driving is at lower speed and there are correspondingly smaller distances between vehicles, the problem occurs that relatively large blind spots exist on both sides of the locating angular range of the radar sensor, since the locating range of the radar first covers the entire vehicle width as of a distance of approximately 8 to 10 m. In the case of very small distances between vehicles, there is therefore the danger that vehicles traveling in an offset manner can no longer be detected, or vehicles cutting in suddenly from the side cannot be detected in time.
It would be desirable, however, to extend the application range of the distance control system to smaller distances between vehicles as well, so that, for example, a so-called stop and go control can be implemented making it possible, for example, during operation in traffic congestion to automatically brake one's own vehicle to a standstill and, when the preceding vehicle drives off again, to automatically control the renewed drive-off of one's own vehicle. Until now, an additional short-range sensor system was needed for this purpose. For example, DE 199 49 409 describes a distance sensor system having two additional distance-resolution short-range radar sensors which are mounted to the right and to the left on the bumper of the vehicle and, given a relatively small locating depth, have a locating angular range of 70° to each side. In the relatively large overlap region of these locating angular ranges, the azimuth angle of an object detected by both sensors can then be determined by triangulation. However, not only is a high installation expenditure requisite for this additional short-range sensor system, but a completely new type of sensor technology and suitably adapted evaluation algorithms becomes necessary as well.